There is conventionally known a twin-path constitution that provides two systems of communication paths, so that when a fault occurs in one communication path, the other communication path is switched over to so as to prevent the communication path from being severed. FIG. 2 shows the twin-path constitution in a conventional wireless communication apparatus. In the wireless communication apparatus (sending side) 101, a LAN (Local Area Network) signal that is input via a layer 2 switch 102 is converted to a wireless frame via a wireless frame converting unit 103. The wireless frame converting unit 103 branches the signal to output an active system main signal 106 and an auxiliary system main signal 107 to an active system modulation/demodulation unit 104 and an auxiliary system modulation/demodulation unit 105, respectively. The active system modulation/demodulation unit 104 and the auxiliary system modulation/demodulation unit 105 transmit the active system main signal 106 and the auxiliary system main signal 107 by wireless communication, respectively.
In a wireless communication apparatus (receiving side) 201, an active system main signal 207 and an auxiliary system main signal 208 that have demodulated by an active system modulation/demodulation unit 202 and an auxiliary system modulation/demodulation unit 203, respectively, are input to a signal selection switch 204. The signal selection switch 204 selects the active system main signal 207, and outputs it via a wireless frame converting unit 205 and a layer 2 switch 206. In the case of a fault occurring in the active system, the signal selection switch 204 switches over so as to select the auxiliary system main signal 208 and outputs it.
Patent Document 1 discloses as a conventional art a channel multiplexing method that enhances availability of the entire network system without revising a device loaded with an existing channel multiplexing technology. This channel multiplexing method, in the case of a fault being detected, interrupts all LAN channels belonging to the same group as the LAN channel in which the fault occurred, presses an information repeater apparatus and a channel multiplexer unit in the terminal to use another LAN channel in which no fault has occurred, and then continues performing the communication.
Patent Document 2 discloses a wireless communication system that transmits a switching signal to a monitor control board of a host station and suspends polling during switchover execution in order to achieve stable monitor control, when switching between an active line and an auxiliary line occurs. By this system, a non-communication state until the timeout for waiting for the response from the slave station is detected can be eliminated, and notification failure of an alarm to the host station or a loss of response of the control can be prevented.